It was many children's idea of the dream birthday party with toy guns, bangers and play fighting.
But the loud bangs and excited screams were mistaken for real gunshots by concerned residents, who called the police.
A squad car arrived and three police officers turned up to the party in the normally quiet village of Yaxham, near Dereham, to investigate.
And when the reality became clear, the police officers stayed to make the party a day Oliver and his friends will never forget, posing for photographs and joining in the fun.
This is the second time in just a month that an incident of reported gunfire was attended by police in Yaxham after the emergency services attended a battle re-enactment at the village's train station in August.
Oliver's mum, Lisa Green, who organised the Nerf gun party, said: 'I was with some of the children's parents who had decided to stay and one of them said a squad car has just pulled onto the driveway.
'The police got out and told me they have had reports of gunfire.
'We had set everything up at the bottom of the garden.
'I told them we have a party going on and they went and had a look.
'They were brilliant with the kids, as soon as they realised it was a children's birthday party they were fab.'
Mrs Green said the children were thrilled to see the police officers arrive at the party and loved being able to ask them questions.
She added: 'The police officers could have just had a look and then left, they didn't have to stay and chat to the kids but they did.
'The kids loved it, they were asking if they were real police officers and they stayed for a little while to talk to them.
'They didn't make a big deal about it at all. The first box of bangers ended up letting off about 25 bangs, we definitely didn't let off the second box.'
A spokesperson for Norfolk Police confirmed that officers from Dereham attended the house at 3.40pm on Saturday after they received a phone call reporting loud bangs which sounded like gunfire.
The police left the premises after around ten minutes and the children were able to continue the fun and games.
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